This invention relates to a platen press for pressing glued press charges, and more particularly, to a platen press which includes a system for maintaining a predetermined spacing between the press platens to thereby control compression of the press charges as the charges are conveyed through a working stretch of the press.
Conventional platen presses, such as the press disclosed in U.S. Pat. No. 3,910,179 to Trouther, include a pair of elongated, vertically spaced press beds, a pair of endless press belts positioned between the press beds, and a pair of endless anti-friction roller belts disposed between the press beds and the press belts. Stationary roller assemblies are positioned at critical locations along the length of the press to control the alignment of the press charge. Lateral edge guides arc provided in known presses to guide the press belts and the press charges as they move through the press. Drive means are connected to the press belts for advancing the belts in the feed direction through a working stretch at a rate predetermined to produce optimal consolidation of the press charge during setting of the glue.
In the type of platen press described above, the press beds, press belts, and anti-friction rollers are massive steel members with high pressures developed at interfaces between these components. Because of these pressures, expensive and intricate bearing systems with hardened steels must be utilized to resist the high contact stresses. Heat transfer to the platens is difficult during press operation because of the limited linear contact between the rollers and platens. Also, it is necessary to use grease as a lubricant to reduce the friction between the rollers, press belts and bedplates. A problem with using grease is that it leaves grease marks, commonly called "tiger stripes," which mar the finished press charge. Grease streaking is deleterious both from a cosmetic standpoint and from a subsequent usage standpoint because the grease affects the subsequent gluability of the surface. Such gluability is critical in the operation of a billet press.
Another drawback with conventional systems is that high contact stresses between the rollers and the platens can result in "football" shaping of billets due to concave platen bowing.
Accordingly, a general object of the present invention is to provide an improved platen press which overcomes the drawbacks and limitations of the prior art proposals. More specifically, the invention has as its objects the following:
(1) to provide a lighter weight press assembly and to reduce the pressure induced friction between press components;
(2) to develop a platen press which eliminates the need to use grease as a lubricant to reduce friction between the components;
(3) to develop a system in which uniform pressure is maintained as the press charge passes through the working stretch;
(4) to provide a platen press which does not require application of heat as the press charge is being conveyed through the press;
(5) to provide a platen press having lower maintenance requirements and a significantly longer press life;
(6) to develop a press which is less expensive and less time consuming to construct;
(7) to develop a platen press which gradually and uniformly applies increasing pressure to a press charge as the charge enters the press; and
(8) the provision of a system for fabricating billets with greater dimensional uniformity than is possible with existing platen presses.